The present invention is directed to detection of impending earthquakes and more particularly, the invention relates to a detector and method for discriminating between general earth tremors and tremors which are precursors to an earthquake. Further, the invention relates to a relay-type earthquake detector for relaying a warning signal to remotely located sensors.
It is well documented that earthquakes have characteristic wave forms and vibration characteristics which are particularly useful for identifying earthquake caliber vibrations from simple random vibrations which are typically encountered in earth formations. Typically, an earthquake tremor results in the propagation of P-(primus) waves, which are propagated as compression and rarefaction and as well involves S-waves (secundus), which waves propagate an orthogonal angle to the direction of the wave. Generally speaking, the P-waves have a natural frequency of approximately 5 Hertz(Hz) while S-waves have a frequency significantly less than the P-waves. The S-waves have a significantly larger amplitude than the P-waves and therefore are the waves that are principally involved in the destruction to structures. P-waves typically travel at a faster rate from an epicenter to a given locale in comparison with S-waves. Thus, detection of P-waves can serve as a warning of the arrival of S-waves at a given location, in particular a location at some remove from the epicenter.
One of the primary difficulties in earthquake detection relates to the time factor involved in detecting tile P-waves. As will be realized, if P-waves can be detected as early as possible, this provides time for evacuation etc., of a building or area in order to avoid potential human injury caused by the arrival of S-waves which, as indicated above, are the chief destructive waves transmitted by geological formations. Early detection of P-waves has conventionally been difficult.
The art has previously proposed various detectors and other arrangements to measure P-waves to portend S-waves. However, in existing arrangements, one of the primary difficulties is providing sensitivity sufficient to detect P-waves at a distance from the epicenter of an earthquake without incurring large costs. A further difficulty has been encountered in that there is often difficulty resolving false alarms from a real earthquake, due to interference in the instrumentation by extraneous vibrations or other frequencies. It is desirable to provide a detector capable of discriminating between P-waves and ordinary, everyday ground and building tremors unrelated to an earthquake. In particular, detectors mounted to a building should be capable of discriminating between the natural vibration frequencies of the building structure, which are a function of the structure, and frequencies indicative of P-waves. The same may be accomplished by means of an information processing unit that stores vibration data and is programmed to discriminate between frequently occurring frequencies and non-regularly occurring frequencies within the range of P-waves.
Typical of the art that has been patented in this field is U.S. Pat. No. 4,689,997, (Windisch). The reference provides a detector which primarily employs a vertical spring barb mounted on a support. A coupler is supported on the other end of the barb and this coupler is connected through a coil spring to a mass positioned in concentricity with the barb and coupler. The spring and mass components are selected to have a natural resonant frequency corresponding to that of an earthquake tremor or other vibration to be detected. A switching circuit is provided to detonate an alarm once the earthquake frequency is detected. Windisch does not provide an integrated circuit mechanism for detection of earth tremors, but rather relies on a mechanical arrangement in the form of a spring and mass system. As is known, such systems are susceptible to temperature fluctuations which can alter the point at which the apparatus can detect the earthquake frequency. Further, the Windisch arrangement does not appear to provide a system which discriminates between simple extraneous vibration and earthquake caliber frequencies.
Caillat et al., in U.S. Pat. No. 5,101,195, provide a discriminating earthquake detector. The arrangement relies on an electromechanical arrangement having a cantilevered device with a predetermined mass on one end. During movement of the beam, an electrical signal is generated which, in turn, is useful for detection of P- and S-waves. Similar to the above-mentioned detectors in the prior art, the arrangement provided in this reference would appear to have limited utility in that there is no provision for a comparison between earthquake caliber waves and those which are simply extraneous, such as would be encountered in traffic vibration, mechanical vibration in a building, aircraft vibration, etc.
U.S. Pat. No. 5,001,466, issued Mar. 19, 1991 to Orlinsky et al., provides an earthquake detector employing an electrically conductive liquid switch means among other variations thereof.
In view of what has been previously proposed in the art, it is clear that there exists a need for a more sophisticated earthquake detector which is discriminatory between extraneous vibration and earthquake level vibration which is not limited in sensitivity.
A further need is for a detector having the ability to communicate both with other like detectors or servers, in order to improve detection capabilities, and remote locations for coordination of earthquake information.
Accuracy of a detector may also be enhanced by having regard to various P-wave characteristics. For example, it has been found that P-waves are indicative of serious earthquakes if they have a duration greater than a certain value. For most locations, this value is approximately 15 milliseconds, although in some locations this is less. Further, it has been found that earthquakes may be predicted with reasonable accuracy if multiple spaced-apart sensors detect P-waves over tile temporal threshold with temporal overlap existing between the detected P-waves.
One object of the present invention is to provide an improved earthquake detector capable of detecting earth tremors at a selected frequency and verifying whether the same are indicative of an imminent earthquake. A further object is to provide a detector system comprising a central processor in communication with multiple spaced apart sensors to further enhance advance warning of an earthquake.
Another object of the present invention is to provide an improved discriminatory earthquake detector for discrimination against natural structural vibrations.
Another object of the present invention is to provide a method of detecting vibration signals indicative of an earthquake, comprising the steps of:
providing a vibration detecting means for detecting vibration signals in a structure responsive to ground vibration, the detection means comprising an integrated circuit including a potentiometer circuit;
mounting the detecting means to the structure;
determining the natural vibration frequencies of the structure;
intermittently comparing electronically any extraneous vibration signal different from the vibration signal of the structure; and
determining whether the extraneous signal is within a predetermined earthquake signal level indicative of P-waves.
The step of determining whether the signal is indicative of P-waves may include measuring electronically the amplitude and duration of the vibration signals and determining whether these exceed predetermined minimum levels.
A further object of the present invention is to provide a method for detecting an earthquake, comprising the steps of: providing an earthquake detector having a first sensor for sensing a selected frequency indicative of an earthquake and a transducer means for transmitting and receiving information and an alarm;
providing a second sensor independent of the first for at least receiving information from the first sensor, the second sensor for verifying information received from the first sensor;
subjecting the first and second sensors to the selected frequency;
transmitting information indicative of the detected frequency from the first server to the second sensor;
processing the information by the sensors; and
activating the alarm means when the frequency is indicative of an earthquake.
Alternatively, the first and second server may independently transmit the vibration detection information to an independent control unit.
In a further aspect, the method comprises the steps of:
providing first and second sensors remotely positioned from each other for sensing a selected vibration frequency indicative of an impending earthquake;
providing communication means for communication between the first and second sensors;
providing a processing unit in communication with the first and second sensors for selecting earth tremor information received from the sensors in the form of a voltage having an amplitude;
subjecting the sensors to the selected frequency and communicating the information indicative of the vibration between the sensors;
selecting within the processing unit a voltage peak indicative of vibrations having an amplitude and duration exceeding selected minimum levels;
assessing any temporal overlap between the selected voltage peaks associated with each of the sensors,
activating alarm means when the amplitude, temporal duration and temporal overlap of the voltage peaks associated with the sensors is indicative of an impending earthquake. Communication between the sensor means and processing unit may be affected by means of wireless or wired electronic communication means, including wireless communication in the infrared or radio frequencies.
Optionally, the processing unit may be remotely positioned from the first and second sensors, and itself incorporate a third sensor.
Conveniently, information from the processing unit can be downloaded to a computer programmed to process the information and optionally transmit the information to corresponding earthquake detectors.
Optionally, the sensors and processing unit can communicate by means of light-emitting diodes (LED""s), or at radio, microwave or IR frequencies.
A further object of the present invention is to provide an integrated circuit electronic detector for detecting any vibration signals of a structure or structures positioned on a substrate, comprising:
detector means for detecting a predetermined vibration signal of the structure and an extraneous signal different from the vibration signal;
amplifier means for amplifying the signal;
comparator means for comparing an extraneous signal with the predetermined vibration signal of the structure to verify whether the extraneous signal is indicative of P-waves; and
potentiometer signal adjustment means for adjusting the detector means to different vibration signals of a structure.
Selectively actuable alarm means may be connected to the comparator means, the alarm means capable of actuation when the extraneous signal is within the predetermined vibration signal.
In a further aspect, the comparator means includes a filter for limiting the detection to vibrations having an amplitude greater than a predetermined minimum and a timer for measuring the duration of said amplitude peaks. The alarm is triggered when the duration of an amplitude peak exceeds a selected amount. For many locations, this selected duration is about 15 milliseconds.
A further object of the present invention is to provide an apparatus for detecting earthquakes and relaying a signal generated therefrom to a remote location, comprising:
an earthquake detector having a first sensor for detecting a frequency indicative of an earthquake and an alarm means actuable at the frequency;
transducer means for relaying and receiving information from the first sensor;
second sensor means remote from the first sensor including a second transducer means for communicating at least with the first sensor; and
a comparator means associated with the earthquake detector for comparing a transmitted signal received by the first sensor with the second sensor for confirmation of an earthquake signal.
The sensors may be linked by any known means for transmissions of electronic signals, including wire linkage and wireless linkage. The latter may include, for example, infrared and radio frequency transmission, for example in the 800-900 megahertz range.
In a further aspect, communication links are established between the units in at least two different frequencies.
In a further aspect, information from the sensors is processed in a logic device for recording vibration information in order to better discriminate against unimportant vibrations, and interfacing with the alarm means for providing an alarm in advance of an earthquake.
In a further aspect, a detector is provided for detecting precursor earthquake tremors, comprising:
first and second sensors for detecting vibrations at a frequency indicative of an impending earthquake;
communication means for transmitting and receiving information between the first and second sensor means;
a comparator means for comparing transmitted signals received by the first and second sensors for confirmation of an impending earthquake signal;
alarm means actuable at the said frequency.
In a further aspect, the apparatus includes a central controller for controlling the operation of the sensors. The controller may also incorporate information storage means for recording and storing vibration tremor information detected by the sensors. The controller may further include a communications port, such as an RS 232 port, permitting an interface of the controller with a computer, which may be programmed with software for storing and processing the earth tremor information.
The controller may be independent of the first and second sensors and may itself incorporate a third sensor.
The transducers within the sensors convert the vibration detected by the sensor into a voltage value, which in turn is transmitted to the controller. A voltage peak above a preselected level is indicative of P-waves affecting the sensor.
The controller preferably includes voltage peak comparison means, for comparing the duration of a voltage peak above a selected limit, indicating a precursor earthquake tremor detected by both (or all three) sensor means, and for assessing any temporal overlap in the voltage peak. The controller further includes filter means whereby voltage peaks having an amplitude above a selected amount are compared for temporal overlap, and voltage peaks having an amplitude below the selected amount are not so subjected. The controller further conveniently includes adjustment means to permit the user to adjust the selected duration cutoff to reflect local earthquake conditions.
Having thus described the invention, reference will now be made to the accompanying drawings illustrating the preferred embodiments.